The Scientific Core will oversee several general aspects of data collection and analysis. First, during the course of the experiments the Scientific Core will arrange for MRI scans to be taken before each animal enters the experiments, 6 months throughout the protocol and finally just before the animals are killed. In this way we will be able to follow the development of some aspects of cerebrovascular disease including the appearance of larger infarcts, edema or small but clinically silent strokes as well as any larger strokes. In addition PET scans will be conducted on a subset of the animals pre-operatively and at 6 months post-operatively and then at 12 months intervals until the animal is killed. These PET scans will provide a direct measure of blood flow that can be related both to the development of changes seen in the MRI scans and in behavior. Second, the Scientific Core will be responsible for collecting all tissues at the time the animal are killed. At that time the animals will be anesthetized and perfused through the heart with ice cold Kreb's buffer during which time the brain, eyes and cerebral blood vessels will be removed. In all cases the brain will be blocked, in situ, in the coronal stereotactic plane and one hemisphere will be flash frozen at -70C while the other will be immersion fixed in 4% buffered paraformaldehyde. The Scientific Core will be responsible for cutting the immersion fixed hemisphere and providing series of sections to Projects 2 and 3. For the eyes, both will be slit at the limbus and one will be immersion fixed in 4% paraformaldehyde while the other will be immersion fixed in 2% paraformaldehyde/2% glutaraldehyde and both will be transferred to Project 4. Finally the cerebral blood vessels will be removed and transferred to project 2 for further analysis. The last responsibility of the Scientific Core will be to maintain a database into which all of the clinical data from the Animal Core, all of the MRI and PET data from the Scientific Core and all of the individual project data will be entered. This databases will be designed in such a way as to facilitate later transfer of some or all of the data to the Main frame for subsequent analysis.